use std::alloc::{GlobalAlloc, Layout};
use std::ptr::null_mut;
use std::sync::atomic::{AtomicPtr, Ordering};
use libc;

struct Block {
    next: *mut Block,
}

struct Page {
    free: *mut Block,
    local_free: *mut Block,
    thread_free: AtomicPtr<Block>,
    used: usize,
}

struct MyAllocator;

unsafe impl GlobalAlloc for MyAllocator {
    unsafe fn alloc(&self, layout: Layout) -> *mut u8 {
        let size = layout.size();
        if size <= 1024 {
            malloc_small(size)
        } else {
            libc::malloc(size) as *mut u8
        }
    }

    unsafe fn dealloc(&self, ptr: *mut u8, layout: Layout) {
        let size = layout.size();
        if size <= 1024 {
            free_small(ptr, size)
        } else {
            libc::free(ptr as *mut libc::c_void)
        }
    }
}

#[global_allocator]
static GLOBAL: MyAllocator = MyAllocator;

fn malloc_small(size: usize) -> *mut u8 {
    let heap = get_thread_local_heap();
    let page = heap.pages_direct[(size + 7) >> 3];
    let block = unsafe { (*page).free };
    if block.is_null() {
        return malloc_generic(heap, size);
    }
    unsafe {
        (*page).free = (*block).next;
        (*page).used += 1;
    }
    block as *mut u8
}

fn free_small(ptr: *mut u8, size: usize) {
    let heap = get_thread_local_heap();
    let page = heap.pages_direct[(size + 7) >> 3];
    let block = ptr as *mut Block;
    unsafe {
        (*block).next = (*page).local_free;
        (*page).local_free = block;
        (*page).used -= 1;
        if (*page).used == 0 {
            page_free(page);
        }
    }
}

fn malloc_generic(heap: *mut Heap, size: usize) -> *mut u8 {
    deferred_free();
    for page in heap.pages[size_class(size)] {
        page_collect(page);
        if unsafe { (*page).used } == 0 {
            page_free(page);
        } else if unsafe { (*page).free }.is_some() {
            return malloc_small(size);
        }
    }
    // allocate a fresh page and malloc from there
    null_mut()
}

fn page_collect(page: *mut Page) {
    unsafe {
        (*page).free = (*page).local_free;
        (*page).local_free = null_mut();
        // move the thread free list atomically
    }
}

fn page_free(page: *mut Page) {
    // Free the page
}

fn get_thread_local_heap() -> *mut Heap {
    // Get the thread-local heap
    null_mut()
}

fn size_class(size: usize) -> usize {
    // Determine the size class for the given size
    0
}

fn deferred_free() {
    // Perform deferred free operations
}

struct Heap {
    pages_direct: [*mut Page; 128],
    pages: Vec<*mut Page>,
}

fn main() {
    let v = vec![1, 2, 3];
    println!("{:?}", v);
}